1. Field of the Invention
The present invention relates to a plasma display panel (PDP), especially an AC type plasma display panel operable in a matrix display system. The present invention is the plasma display panel of suitably used for a surface discharge type PDP in which discharge will occur along a screen.
2. Description of the Related Art
Recently, plasma display panels (PDPs) have been widely used in television displays as well as monitors of computers since color PDP screens could be practically available. Particularly, these PDPs may be utilized as large-screen flat type display devices for the high definition television (HDTV) system.
In matrix display type PDPs, a memory effect is utilized so as to sustain lighting conditions of cells. The AC type PDP is arranged so as to own a memory function in a structural manner by covering an electrode with a dielectric material. That is, when the AC type PDP is turned ON, lines are successively addressed in order to store wall electron charges only into cells to be lighted(emitted). Thereafter, voltages (namely sustain voltages) having alternate polarities are applied to all of these cells within one time. This sustain voltage corresponds to a predetermined voltage lower than a discharge starting voltage. In such a cell where wall electron charges are stored, since the wall voltage is superimposed with the sustain voltage, the effective voltage applied to this cell exceeds the discharge starting voltage, so that a discharge operation will occur. If the time period during which the sustain voltage is applied is shortened, then a virtually continuous lighting condition can be obtained.
In surface discharge type PDPs which are commercially available, one pair of sustain electrodes (namely, first electrode and second electrode) are arranged in parallel to each other, which extend over and entire length of the screen in a matrix display every line, whereas an address electrode (namely, third electrode) is arranged every column. An interval between sustain electrodes in the respective lines is referred to as a "discharge slit". A width of this discharge slit is selected to be such a value, for example, 50 to 100 .mu.m that the surface discharge may occur when the effective voltage of on the order of 200 to 250 V is applied. On the other hand, another interval between sustain electrodes present in adjacent lines is referred to as a "reverse slit". A width of this reverse slit is made sufficiently larger than that of the discharge slit. That is to say, the surface discharge occurred between the sustain electrodes separated from each other via the reverse slit can be prevented. As described above, both the discharge slit and the reverse slit are provided to arrange the sustain electrodes, so that the respective lines can be selectively emitted.
A protection film having an anti-sputtering characteristic capable of mitigating an influence caused by ion bombardment occurred during discharge operation is provided on a surface of a dielectric material layer (for instance, a low melting point glass) for covering the sustain electrode. Since this protection film is made in contact with the discharge gas, both a material of this protection film and a film quality thereof may give great influences to the discharge characteristic. In general, magnesium oxide is employed as a protection film material. Magnesium oxide corresponds to such an insulating material having the superior anti-sputtering characteristic and the large secondary electron emission coefficient. In other words, since magnesium oxide is used, the discharge starting voltage is lowered, so that the surface discharge type PDP can be readily driven. Recently, a magnesium oxide film having a thickness of on the order of 1 .mu.m is formed on a surface of the dielectric material layer by performing a vacuum vapor deposition while using magnesium oxide made in a pallet form as a starting material.
When the surface discharge type PDP is driven, a charge distribution over an entire screen is initialized (reset) during a time period defined after the sustain voltage application for a certain image is accomplished until a next image is addressed. Concretely speaking, prior to the addressing operation, reset pulses whose peak values exceed the discharge starting voltage are applied to the sustain electrode pairs of all of the lines. Since the reset pulses are applied, the surface discharge phenomenon will occur at front edges of these reset pulses, so that a large amount of wall electron charges are charged to the respective cells rather than that of the sustain voltage application. Subsequently, the self-discharge phenomenon will occur, which is caused only by the wall voltage in response to the rear edges of the reset pulses. As a result, the most wall charges are neutralized, and thus will disappear. In other words, the dielectric materials over the entire screen are brought into the substantially non-charged condition. Alternatively, another initialization may be carried out without such a self-discharge operation by that an erasing/discharge phenomenon occurs only in the cells which have been previously, selectively charged. In this alternative case, the addressing operation for this initialization is required, so that time required for switching displays would be prolonged.
Conventionally, there is another problem that a display is disturbed, called as a "black noise". The "black noise" is such a phenomenon that a cell to be lighted (namely, selected cell) could not be lighted. This black noise may easily occur in a boundary between a lighting region and a non-lighting region within a screen. It is not a fact that all of the plural selected cells contained in either one line or one column are not lighted. However, since the black noise occurrence portions appear in some places, the occurrence reason of this black noise may be understood as an address missing phenomenon. This address missing phenomenon is caused by that no address discharge operation is executed, or even when the address discharge operation is performed, the strength thereof is low.
The reason why the address missing phenomenon may be conceived by the residual wall charges in the reverse slit. In the case that the surface discharge operation is excessively spread by receiving the reset pulses and thus the wall charges are stored also in the reverse slit, even when the self-erasing discharge operation is subsequently performed, the wall charges present at the reverse slit located far from the discharge slit are left. The effective voltage of the addressing operation is lowered by this residual charge, so that the address missing phenomenon will occur. If the neighboring cells are the selected cells, since the space charges caused by the address discharge operations at the neighboring cells may contribute the priming effect, the address missing phenomenon can hardly occur. To the contrary, in the case that the neighboring cells (especially, front side of scanning) are the non-selected cells as in the above-described boundary, no priming effect may occur. Thus, the address missing phenomenon can hardly occur.